In recent years, a nonlinear Raman scattering detection apparatus using a nonlinear optical process has been proposed as an apparatus capable of having a detection time shorter than that in a spontaneous Raman scattering detection apparatus. PTL 1 describes a stimulated Raman scattering (SRS) microscope as the nonlinear Raman scattering detection apparatus. This SRS microscope can emit pulsed light beams of two colors having different optical frequencies (wavelengths) to a sample, extract a produced change in pulsed light intensity as an SRS signal by lock-in detection, and thus identify and distinguish molecules included in the sample.
The SRS microscope described in PTL 1 reduces noise in pulsed light intensity by splitting an optical path of one of the pulsed light beams of two colors into two components, providing a time delay to one of the components, and then combining them.